Nylon is an extremely important plastic polymer
that's used to make clothing
and a whole bunch of other products.
There are a few different types of nylon
and the one that I wanna make
is specifically known as Nylon 6,6.
In order to make it
I'm going to be following this reaction scheme
which is the typical industrial route to Nylon 6,6.
On the left side
it starts with cyclohexanol
which is converted to adipic acid
and then to adipoyl chloride.
The adipoyl chloride
is then reacted with hexamethylenediamine
to form the final Nylon 6,6.
The reason why we call it Nylon 6,6
is because each of the precursors
(i.e. the hexamethylenediamine and the adipoyl chloride)
both have 6 carbons in them.
Unfortunately, I don't have a reasonable way to make the hexamethylenediamine
and I'm just gonna have to buy it.
Because of this,
I'm gonna be focusing almost entirely
on this left side of the reaction scheme
starting with cyclohexanol.
Cyclohexanol is typically converted into adipic acid
by heating it in nitric acid
along with a metal catalyst.
However, this produces a lot of nitrous oxide gas
which contributes to both global warming
and the depletion of the ozone [layer].
For many reactions,
this wouldn't really be a huge issue
but adipic acid is produced on a massive scale.
Despite efforts to trap, recycle, or neutralize the nitrous oxide,
this process still releases
more than 400,000 metric tons per year.
The wastefulness of this method is not unique
and there are countless more industrial processes like it.
Fortunately, in the past few decades,
we've become more environmentally aware
and a lot of effort has been put in
to making cleaner and more efficient methods.
This effort has spawned a relatively recent
but a very popular area of chemistry
known as "green chemistry".
The main goal of green chemistry
is to reduce or eliminate
the use and production of hazardous waste materials.
Anyway, with green chem in mind,
I decided to make adipic acid
in a more environmentally friendly way.
With a little bit of searching,
I found a modified method
that doesn't produce any nitrous oxide
but is supposed to have the same or better yields.
In the old synthesis,
I would have used nitric acid,
a metal catalyst,
and cyclohexanol.
In the reaction,
the nitric acid is being used as an oxidizing agent,
but the problem with it
is that it's also the source of the nitrous oxide gas.
In this new prep,
we still need to use a metal catalyst
and cyclohexanol,
but instead of using nitric acid here,
it's swapped for a new oxidizer — hydrogen peroxide.
With hydrogen peroxide,
the reaction won't release any nitrous oxide gas,
and the only thing that comes off is going to be oxygen.
On top of this,
the reaction mixture is recyclable.
Once the reaction's done,
we can add a little bit more peroxide,
add some more cyclohexanol,
and the reaction can be repeated.
The old method is kind of a one-and-done kind of deal.
So this modified method not only eliminates the release of nitrous oxide gas,
but it also reduces waste
because the reaction waste can be used in multiple cycles.
Okay, so, getting started with the reaction,
everything I used is shown here.
On the left, I have 30% hydrogen peroxide,
in the middle I have some powder tungsten metal,
and on the right is the cyclohexanol.
The tungsten metal and the cyclohexanol were purchased from eBay,
but I had to get the peroxide locally.
The procedure that I'm following is from a paper found online,
and I'll provide a link to it in the description.
The tungsten metal is not used directly in the prep,
and before starting,
it needs to be converted into tungstic acid.
Luckily for me, this is actually pretty easy to do.
Into a small beaker,
I add a stir bar
and about 40 mL of hydrogen peroxide.
I then add a small amount of tungsten powder.
I turn on the stirring, but I don't turn on the heating,
because the reaction between the tungsten metal and the peroxide is exothermic.
The reaction at room temperature is slow,
but as they react and generate heat,
the reaction will speed up.
As the solution gets hotter,
we'll start to see steam coming off
and a bunch of bubbling.
Anyway, what we have going on here
is hydrogen peroxide reacting with the tungsten metal
to form tungstic acid.
Tungstic acid is normally insoluble in water,
but in the presence of peroxide,
it forms a water-soluble complex.
As far as I know,
this complex doesn't really have a name,
but it's the active catalyst for the reaction.
The reaction is done
when it doesn't look like there is any tungsten left.
My solution here is murky,
and in theory it should be perfectly clear,
but I think my tungsten metal wasn't very pure.
I quickly set up the reaction flask,
and I added the catalyst to it.
I washed the beaker
with a decent amount of hydrogen peroxide,
and I transfer this to the flask as well.
With the catalyst in the flask,
I then top it off with a bunch more peroxide.
With the catalyst,
and all the hydrogen peroxide loaded in the flask,
it's time to add the cyclohexanol.
With strong stirring,
I pour in around 100 g,
and the solution quickly becomes white.
Cyclohexanol is not very soluble in water,
so with the stirring,
we get a very fine and opaque dispersion.
If I turn off the stirring,
it should clear up,
and the cyclohexanol would separate
as a layer above the water.
The reaction doesn't really happen at room temperature,
and to get things going, we need to heat it up.
The target temperature is 90℃,
and I need to hold it there for about 20 hours.
For this reaction,
temperature control is very important,
which is why I have the thermometer in the left neck.
In the middle, I have a condenser
which should re-condense any vapors that come off.
It's important to have the condenser,
because the reaction is kept at a high temperature
for a long period of time.
If no condenser was used,
most of the water would probably evaporate
before we even got to the 20-hour mark.
Anyway, continuing with the reaction,
I turn on the heating mantle,
and I slowly raise the temperature to the 90℃ mark.
When it got to about 85℃,
the bubbling just took off,
and the temperature spiked to about 100.
I had to quickly remove the heating mantle,
and cool things down using some cold water.
This was really unexpected
because I was following a paper
and it never mentioned anything like this happening.
Anyway, the cold water worked pretty well
and the reaction quickly slowed down.
Without the stirring,
the cyclohexanol separates,
and you can see that it forms a layer above the hydrogen peroxide.
The reaction was cooled down to about 85℃,
but it very quickly took off again.
For the next 5 hours,
it was a cycle of cooling it down
and then letting it heat up again.
The fact that this isn't mentioned at all in the paper
really makes me think that something weird is going on.
Anyway, this is the reaction
that's supposed to be occurring.
In the presence of the tungsten catalyst
and hydrogen peroxide,
the cyclohexanol is being oxidized to adipic acid.
In terms of the mechanism,
this was what was suggested
by the authors of the paper.
It starts with cyclohexanol,
which is oxidized by peroxide
to form cyclohexanone.
The cyclohexanone then undergoes a Baeyer-Villiger reaction,
which converts the cyclic ketone to a lactone group.
The caprolactone is slowly hydrolyzed by water,
which breaks apart the ring
and forms 6-hydroxycaproic acid.
The hydroxyl group is then further oxidized
to form an aldehyde.
In the final step,
the aldehyde group is oxidized to a carboxylic acid,
which gives us the final adipic acid.
Eventually, the reaction got more under control,
and I was able to stir it like this for the next 2 or 3 hours.
The temperature remained pretty constant
at around 94℃.
After a few hours of stirring,
the reaction died down
and the temperature began to drop.
I turned up the stirring,
and this time,
you can see no layer of cyclohexanol forms at the top,
and we actually have some stuff forming at the bottom.
When I stopped the stirring earlier,
a layer of cyclohexanol formed at the top,
but apparently that's all gone now.
Because the temperature was dropping,
I put the heating mantle back on,
and I started to heat things again.
I really thought that the bulk of the reaction was over,
but once I got around to 85–90℃,
the reaction took off again.
It didn't get too crazy,
so just like before,
I just kept stirring it.
The temperature rose to about 95℃,
and then remained pretty constant.
Over the next 2 hours,
the solution slowly cleared up,
and started to look kind of like a lava lamp.
I don't think it's working in the same way though,
because lava lamps require a gradient in temperature,
where it's hot on the bottom and cold at the top.
In a lava lamp,
wax gets hot on the bottom
which reduces its density,
so it floats to the top,
where it cools,
increases its density,
and sinks back down.
In my case, I have really strong stirring,
so the temperature must be more or less uniform.
I'm not exactly sure what's happening,
but I think oxygen bubbles
are pulling the globs to the surface,
then once the globs lose the oxygen,
they sink back down.
I honestly have no idea what these globs are,
but whatever they are,
they have to be denser
than the hydrogen peroxide solution.
All of the intermediates
that were suggested in the paper
don't have a density higher than that of hydrogen peroxide,
so I honestly have no idea what this is.
Just for fun, I turned off the stirring,
so I can get the full lava lamp effect.
As the globs fall down,
they coalesce around the stir bar,
and I think it's much clearer here
that the bubbles are just carrying the globs
back to the surface.
I crank up the stirring again,
and over the course of the next hour or so,
most of the globs disappear.
I also started to see something crystallize on the sides of the flask.
At first, I thought these were adipic acid crystals,
but I don't think they are.
Anyway, the temperature started to decrease,
and I actually needed the heating mantle from this point on.
I removed the stopper and I smelled the vapors,
and the stench was unmistakable.
What I'm smelling here is 6-hydroxycaproic acid,
which is kinda of a musty vomit-like smell.
Although it's stinky, it's still a good sign,
because it means we're getting close
to the final adipic acid.
Around the 15-hour mark,
the solution started to become opaque,
as adipic acid precipitated out.
Over the course of the next 5 hours,
a lot more adipic acid was formed,
but it was more or less pretty mundane.
At the 20-hour mark,
I took off the heating mantle,
and I let the mixture cool overnight.
I came back around 12 hours later,
and we can see a lot of adipic acid on the bottom.
To get out as much adipic acid as possible,
I placed the flask in a freezer for about an hour.
I then filtered it off using my 1L funnel,
that was flagged by customs
and then investigated by the RCMP.
I used as little water as possible
to transfer everything from the flask to the funnel.
I washed the sides with a little bit of distilled water,
and then I mixed things around to wash the adipic acid.
I only did one washing step,
but in hindsight I really should have done more,
and you'll see why in a few minutes.
Once I was done washing it,
I left the vacuum pump running
to dry it up as much as possible.
I was left with some crude and relatively dry adipic acid,
which I transferred to a beaker.
The adipic acid isn't very pure right now,
and to clean it up, I need to do a recrystallization.
I have about 95 g of crude adipic acid,
and I found a resource online
that said it could be recrystallized in 2.5 times its weight in water.
I don't add the water all at once,
and I start by adding about 200 mL.
I turn on the hot plate and the stirring,
and I wait for things to heat up.
When it got close to boiling,
I added the final 50 mL,
and I waited for it to boil again.
The solution was supposed to clear up after all the water was added,
but it stayed opaque.
I tried adding a bunch more water to try to get things to dissolve,
but it didn't really do much of anything.
There's some sort of white impurity floating around
that isn't dissolving,
and I need to get rid of it somehow.
I tried to do a hot filtration
through a couple coffee filters,
and that clearly didn't work.
I tried to pull it through a Büchner funnel
that was packed with very fine filter paper,
but that didn't work either.
This is the only thing that seemed to work decently.
The solution was reboiled,
and I let it stand for the solid to sink to the bottom.
I then poured off the liquid, and I left behind the solid stuff.
Unfortunately, I don't think it's easy to clean up further,
so I just let it crystallize.
Because the solution was opaque,
the crystallization wasn't very pretty to look at.
After it cooled down to room temperature,
I put in in the freezer and chilled it to around 0℃.
I then brought back my glass Büchner funnel,
loaded it with a filter paper,
and filtered off all of my adipic acid.
All of the impurities that made the solution opaque
should still be present,
and because they passed through the filter,
I figured that I could probably wash them away here.
So using ice-cold water,
I washed the adipic acid a few times.
In the flask below,
you can see that what I'm collecting is opaque.
Unfortunately, adipic acid is minorly soluble in water,
so I have to make sure that I don't overdo the washings.
There's definitely some of this impurity still left over,
but there's not much I can do.
I'm hoping I can purify it out in the next step,
when I make adipoyl chloride.
So to move on,
I pulled a vacuum for a few minutes
to try to dry things up as much as possible.
The adipic acid was transferred to a piece of printer paper,
with some paper towel underneath.
I left it out for about a day or two,
and I was left with a nice, dry powder.
The final yield was about 50 g of adipic acid,
and this is extremely low.
On top of this,
I measured the purity by taking the melting point,
and what I have here is not very pure.
The paper I'm following advertised a yield of 127 g,
and it also said that it would be quite pure.
I did a little bit of investigating,
and I think I found out why my yield was so low,
and it has nothing to do with the paper.
The major reason seemed to be really bad quality cyclohexanol.
Pure cyclohexanol has a melting point around 26℃,
so it's pretty common for it to be solid at around room temperature,
which is around 20℃.
While the cyclohexanol that I have
doesn't begin to solidify below 26℃,
it starts to solidify below -3℃.
It was supposed to be pretty pure,
but if it's solidifying nearly 30℃ below the melting point,
well, it's definitely pretty dirty.
This might explain why the reaction took off in the beginning,
because maybe the peroxide was reacting with
something else in the cyclohexanol.
This also might have led to the formation
of all of that white and soluble stuff at the end.
The impurity likely represented a large percentage of the cyclohexanol,
and this would inevitably impact the yield.
So with all of that being said,
I think it's a good idea to redistill the cyclohexanol,
before doing this reaction.
It didn't suggest to do this in the paper,
and unfortunately it didn't occur to me at all.
In the end though,
50 g of adipic acid is more than I need,
so I'm not gonna bother repeating this.
I have a feeling that if I were to redistill my cyclohexanol,
and do the whole thing over again,
it would go exactly as it described in the paper.
Anyway, as I said before,
the next thing that I need to do
is convert it into adipoyl chloride.
To do this , I need to use the chemical thionyl chloride,
which has just been sitting around
and waiting for me to use for about a year now.
The next video is either going to be the adipoyl chloride one,
or I'm going to continue recycling my mercury,
and convert the mercury sulfide I got from the previous video
back to mercury metal.
Also, I finally received my NileRed beakers,
and I've opened up a shop online.
The website is just nilered.ca,
and if any of you are interested in checking it out,
there's a link in the description.
Right now, the site only accepts orders
from Canada or the US,
so if you're from somewhere else
and you want to get something,
just send me an email at this address here.
(admin@nilered.ca)
So as usual,
I'd like to thank everyone
who's supporting me on Patreon.
Everyone who supports me
will see my videos
24 hours before I release them to YouTube.
On top of this, all of my supporters
can directly message me on Patreon,
with any questions or comments that they have.
And I do my best to respond within about a day or so
to all of my Patreon messages.
Also, if you support me with $5 or more,
you'll get your name at the end of the video
like you see here.
Here's just a small list of some of the future videos I'll post,
if you guys have any other ideas, please let me know in the comments.